Oil discussions come close to politics and religion. So please consider the following as "Opinion" mine, of course, but still opinion. Any one remember EP oil from about the late 1960's to the middle 1970's? I know I am dating myself. We used it for the leaky 216 in my truck and my brothers GMC(engine unknown). Cheap and purchased by the case. A bit like a slow motion oil change(hey look ma no filter on these motors). Worked fine. Pennzoil(yep that brand), was a common oil used by many at the same time. Problems? Some had huge sludge build up in the valve covers and around the valves and springs. Other wise...none. The difference from then and now? Detergent oil. And the odd PCV system. Conclusions? Detergents work(this used to be a hot oil topic) PCV? It works too. The engines I see are cleaner, much cleaner. Most of the sludge was from short hops(water condensation) But that detergent stuff makes a difference. Look at the API codes. Spend what you need and drive it. Synthetics work in properly sealed motors, and last because the contaminations are better controlled(do not expect that to happen just because you rebuilt a 65 year old motor). The one advantage synthetic oil has, the polymer is longer and stronger. The other less often noticed difference is the viscosity is a bit more stable over a wider temperature range. My 2 cents have been spent, enjoy.
